Particle separation utilizing a magnetized fluid



Sept 1, 1959 J. GREEN 2,902,153

PARTICLE SEPARATION UTILIZI NG A MAGNETIZED FLUID Filed April 20, 1956 III INVENTOR JACK GREEN United States Patent O 2902,153 PARTICLE SEPARATION UTILIZING A MAGNETIVZED FLUID Jack Green, La Habra, Califi, assignor'to" California Research Corporation, San Francisco, Calif., a corporation of Delaware Application April 20, 1956, Serial No. 579,559

12 Claims. (Cl. 209-208) separation on the basis of size and density, various screening arrangements for separation o'n'the basis of particle size, numerous magnetic separation systems for separating magnetic and nonmagnetic materials, and flotation methods for separating homopolar from nonhomopolar substances.

There are numerous applications Where precise separation of particles in accordance with their density and/or shape is required. One of such applications is in theseparation of mineral particles in geochemic'al'work and in standard mineral dressing techniques; For example, in some geochemical problems it may be desirable to separate zircons from a sand matrix, micas with inclusions from Inicas without inclusions, or clouded feldspars from unclouded feldspars. In mineral dressing practices it may be desirable to separate, say, iron-rich sphalerites from iron-free sphalerites, or possibly, cobalt-rich pyritefrom pure pyrite. These separations, even using flotation methods, have heretofore been virtually impossible to perform at a reasonable cost and with speed and accuracy because of the minute differences in densities in many cases. The use of screens forsuch separations is not practical, owing to the fact that the volume of the different particles is not necessarily directly related to the density thereof. In addition to the above-listed examples of particle separation, there are numerous other applications in which it is desired to perform precise separation of nonmagnetic particles without resorting to laborious manual sorting.

Broadly the present invention contemplates methods and apparatus for separating nonmagnetic particles according to density and shape parameters in which the material is placed in a substantially vertical tube which contains a suspension of a magnetic material colloidally dispersed in a suitable liquid. A first electromagnetic coil disposed along the length of the tube produces a first electromagnetic field in the colloidal suspension, and the strength of this electromagnetic field varies progressively along the length of the tube. The electromagnetic field reacts with the magnetic particles in the colloidal suspension to vary the viscosity of the fluidas a function of the strength of this electromagnetic field. This phenomenon of varying the viscosity of a colloidal suspension containing magnetic particles in response to-the application of an electromagnetic field is fairlywell known, and is utilized in the so-called magnetic fluid clutch and other similar applications.

In one embodiment, the spiral coil winding ofthe first electromagnetic coil is so disposed that the viscosity of the colloidal suspension progressively increases down-.

Wardly of the tube. The material to be separated is then introduced into the t'opof the column of'solution, and

the nonmagnetic particles distribute themselves in the variable viscosity, colloidal suspension at a rate determined by' their density.- According to the nature of the material to be separated, approximate or discrete size fractions may be prepared by screening priorto introduction of the material into the tube, although in some cases this step may not be necessary'l' This method'is particularly effective in certain'g'eochemical applications in which it producesfan exaggerated separation of low density," layer lattice mineral particles, such as micas, with respect to the high density "nonlayer lattice'minerals, such as garnets. After a suitable time period, an optimum degree of separation of the different particles occurs. The length of this period "will be dependent upon the characteristics of the electromagnetic field, which characteristics may be varied at will, the properties of the iron-fluid colloidal suspension and the shape and density parameters of the material to be separated.

When the optimum separation has been reached, an

additional set of secondary electromagnetic coils is energized'to produce a plurality of localized electromagnetic fields at different zones along the length of the tube. These localized electromagnetic fields 'are of considerably greater magnitude than the first electromagnetic field ng and they act to elfectively solidify the colloidal suspension into a plurality ofspaced disks, each disk having a location corresponding to a zone of application of a respective secondary field. This solidification physically segregates the fractions which have already been separated by the variable viscosity of thecolloidal suspension. The first electromagnetic field is then removed and the colloidal suspension together with the entrained particles of nonmagnetic'material is drawn out of the tube atohe or more points between the solidified disks to obtain the desired density fraction or fractions of the separated nonmagnetic particles. For some materials, separation "of constituents may occur as a function of shape. The separated material is then collected on a suitable filter or screen which permits the iron-fluid colloidal suspension to pass through into a recirculating unit As an additional refinement of the present invention, the drawn-off solution may be subjected to an additional electromagnetic field which removes'an'y magnetic particles present in the colloidal suspension. u p I The objects and advantages of the present invention will be further apparent from the following description When read inconnection with the accompanying drawing, the single figure of which diagrammatically illustrates one embodiment of the present invention.

Referring to the drawing by character of reference,

numeral 11 designates a hollow tube of suitable material, such as glass, Bakelite, aluminum, or steel, in which the suspension is disposed. Tube 11 is provided with 'an' thereof, with a colloidal suspension 13 comprising particles of a highly magnetic material, such as iron, colloidally dispersed in a suitable liquid such as glycerine, oil, Water, silicone oil, or kerosene. The'initial concentration of iron'insuspension may be varied to produce a series of iron suspensionswhich'may be used accord ing to the gross density-shape parameters of the material to be separated. Care should be. taken. to avoid the- 3 P e of an chsmisa ly reactive sub a su h as sulphur, in the suspending fluid. In some instances, the dispersion of magnetic particles in the suspending fluid a esu t n a ettl n and ak n of h m g et p ticles over a period of time. netic particles may be treated with a wetting agent which surrounds each particle with a layer of fluid, so that a slight mixing of the dispersion results in a homogenous mixture.

Tube 11 is surrounded along its length by a first electromagnetic coil 16. The spacing between the turns of coil 16 progressively decreases downwardly of tubing 11 so that the strength of the electromagnetic field Produced in colloidal suspension 13 by coil 16 will progressively increase downwardly of tube 11. Coil 16 is energized from a suitable source of current such as a battery 21 connected to a potentiometer 22. The electromagnetic field produced by coil 16 magnetizes the magnetic particles in colloidal suspension 13 to cause the viscosity of colloidal suspension 13 to progressively increase in the direction of the progressively increasing electromagnetic field.

A plurality of secondary electromagnetic coils 23a, 23b, 23c, 23d, and 23e surround tube 11 at spaced zones along the length thereof. Coils 23a through 23c each preferably comprise only a few closely spaced turns so as to localize the effects of their electromagnetic fields at zones corresponding to the locations of the coils themselves. Coils 23a through 23s are energized in parallel from a suitable current source such as a battery 24 connected to a potentiometer 25. The current supplied to coils 23a through 23e is preferably several orders of magnitude greater than that supplied to coil 16. The currents in secondary coils 2311 through 23c may be controlled independently of each other by means of individual adjustable resistors, as shown. In some cases it may be desirable to keep the currents in these coils at a level below that necessary to produce solid disks. For example, highly viscous disks may enhance the separation of substances of widely diflFerent density or shape parameters.

Tube 11 is also provided along its length with a plurality of outlet lines or spigots 26a, 26b, 26c, 26d, and 262, which preferably extend into approximately the center of tube 11, for withdrawing selected portions of the colloida suspension in tube 11. Suitable means are also provided for conducting the drawn-off solution from the spigot to a suitable container. Such means may be in the form of a sluice 27 communicating with a suit.- able sieve or filter 28 on which the separated fraction may collect, permitting the colloidal suspension to pass through and be recirculated through a funnel and conduit 33. An additional electromagnetic coil 31 connected to a battery 32. may be provided below sluice 27 for removing the magnetic particles in the drawn-01f colloidal suspension. Although sluice 27, filter 28, coil 31, and recirculation conduit 33 have been illustrated only in connection with spigot 26c, it will be understood that similar means will be provided in association with the other spigots.

In operation of the embodiment illustrated in the drawing, after placing the colloidal solution or suspension of colloidally dispersed magnetic materials in tube 11, coil 16 is energized to produce an electromagnetic field in the colloidal suspension, the strength of this magnetic field progressively increasing in value downwardly of tube 11. This progressively increasing electromagnetic field produces a corresponding progressive increase in the viscosity of the solution downwardly of tube 11. The magnitude of the electromagnetic field .of the spiral windings of coil 16 may be adjusted by means of the potentiometer 22 .to make initial gross density separations, or may be so adjusted as to enhance separation according to the specific density-shape parameters of the material to be separated. When desired, this adjustment To a id s, e as 4- a b a so p shcd raduall and omat y u 'n the separation process by adjustment of potentiometer 22.

The material to be sorted is then introduced into the top of tube 11 from hopper 20 and permitted to distribute itself in the variable viscosity solution at a rate in accordance with the density and/ or shape of the nonmagnetic particles. After an optimum time period when the desired separation of particles in the variable viscosity or colloidal suspension is reached, coils 23a through 23e are energized to provide localized electromagnetic fields of high intensity at the locations of these coils. These coils effectively solidify the colloidal suspension into a plurality of disks at zones along the length of tube 11 corresponding to the location of coils 23a through 2342. These disks form effective physical barriers be- Ween which the material to be separated is distributed in density and/or shape fractions.

After this solidification, coil 16 may be deenergized and one or more of spigots 26a through 2642 may be opened to draw off the colloidal suspension to obtain the desired density and/or shape fraction. In this connection, suitable stoppered openings (not shown) may be provided in tube 11 to permit the entry of air during drainage of the different fractions.

Stokes law of fluid mechanics relates the density and size of a particle to the density and viscosity of the fluid in which the particle falls:

where:

V is velocity in cm./sec.

g is acceleration due to gravity in cut/sec.

a is the radius of the particle considered as a sphere d is the density of the particle d is the density of the medium 1; is the coefiicient of viscosity of the medium.

As a consequence of this law and the fact that the viscosity of the medium will progressively increase downwardly in tube 11, progressively denser fractions of particles may be withdrawn from spigots 26a, 26b, 26c, 26d, and 26e, respectively, per unit time. Similarly, it will be obvious that for a given length of tube 11, the number and spacing of coils 23a through 232 will determine the number of clilferent density fractions obtainable, as well as the density range within a given fraction. Also, for a given length of tube 11 the number and spacing of coils 23a through 23c will determine, for certain materials, both the number of diflerent fractions obtainable based on shape parameters and the index of sphericity range within a given fraction. Furthermore, the fields produced by coils 23a through 23c are localized as much as possible to produce as thin disks as practical. As the solution is drawn off, electromagnetic coil 31 may be energized from battery 32 to magnetically remove the magnetic particles in the drawn-elf solution.

In an alternate embodiment of the present invention, the direction of variation of the strength of the first electromagnetic field is reversed with respect to its direction of variation in the embodiment illustrated in the drawing. That is, the turns of the coil are more closely spaced at the top of the tube than at the bottom, thus producing an electromagnetic field which increases in strength upwardly in the tube and resulting in a progressive increase in the viscosity of the magnetized solution upwardly in the tube. In this case, the material to be separated is introduced into the top of the tube and permitted to settleat a rate determined by the density and space parameters of the particles. The separation is performed on a rate of settling basis by energizing the secondary electromagnetic coils at a predetermined time after introduction of the material in the tube. The time interval between introduction and energization will be dependent upon the degree of separation required, the

characteristics of the separatedmaterialand the viscosity interval can be selected which will result in the desired erit to those skilled in the art that various changes and modifications may be made therein-without departing from the spirit of the invention orfthelscope of the appended claims.

Iclaim, 1. The method of separating particles of. a non-magnetic material according to density and shapeparameters comprising the steps of forminga column of a suspension of particles of a magnetic material colloidally dispersed in a liquid, applying a first electromagnetic field to said suspension to magnetize'said particles of magnetic material, varying the strengthfof said first field along the length of said column to cause the viscosity of said suspension to vary progressively along the length of. said column, inserting said particles of a nonmagnetic,

terial in the top of said column to cause said particle'sof a nonmagnetic material to 'distribu'te themselves in said variable viscosity suspension in accordance with their density and shape parameters, applying'a second'electromagnetic field to at least two spaced-apart zones along the length of said'column to effectively solidify said suspension at said zones, and withdrawing from said column the suspension and particles of nonmagnetic material,

between said effectively solidified zones.

2. The method of separating particles of a nonmag netic material according to densityand shapepara'meters comprising the steps of forming a column of a suspension of particles of a magnetic material colloidally dispersed inv a liquid, applying a first electromagnetic field to said suspension to magnetize said particles of magnetic material, varying the strength of said first field along the length of said column to cause the viscosity of said suspension to vary progressively along'the ange of said column, inserting said particles of nonmagnetic material to be separated in the top of said column to cause said particles of nonmagnetic material to be distributed in said variable viscosity suspension in accord ance with their density and shapejparameters, applying a second electromagnetic field to at least two spaced apart zones along the length of said column to effectively solidify said suspension at said zones, withdrawing from said column the portions of said suspension and particles of nonmagnetic material between said effectively solidified zones, and removing from said withdrawn por tions the nonmagnetic particles contained therein.

3. The method of separating particles of a nonmagnetic material according to density and shape parameters comprising the steps of forming a column of a suspension of magnetic material colloidally dispersed in a liquid, applying a first electromagnetic field to said suspension, varying the strength of said first field along the length of said column to cause the viscosity of said suspension to vary progressively along the length of said column, inserting said particles to be separated in the top of said column to cause said particles to fall through said variable viscosity suspension at a rate determined by their density and shape parameters,'applying a second electromagnetic field to at least two spaced-apart zones along the length of said column at a predetermined time after the introduction into said column of said particles to be separated to efiectively solidify said suspension at said zones, and withdrawing from said column the suspension and particles of nonmagnetic material between said efiectively solidified zones.

4. The method of separating particles of a nonmagnetic material according to density and shape parameters comprising the steps of forming a substantially vertical embodiments the present invention have been described, it will be appar-' field to at least two spaced-apart zones along the length of said column at a predetermined time after. the introduction into said column of said particles to be separated to effectively solidify said suspension at said zones, and withdrawing from said column the suspension and particles of nonmagnetic material between said efiectively solidified zones. 7

5. Apparatus for separating particles of a nonmagnetic material according to density and shape parameters comprising a tube containing a suspension of magnetic material colloidally dispersed in a liquid, at first electromagnetic coil disposed along the length of said tube for producing an electromagnetic field in said suspension,

means for varying the strength of said electromagnetic field along the length of said tube to cause the viscosity of said suspension to vary progressively along the length of'said tube, means for introducing said particles of-nonmagnetic material in said tube to cause said particles of nonmagnetic material to be distributed in said variable viscosity suspension inaccordance with their density and shape parameters, a plurality of second electromagnetic coils disposed about said tube at zones spaced along the length thereof, means for energizing said second coils to produce a plurality of spaced electromagnetic fields which effectively solidify said suspension into a pluralityof discs at said zones, and means for withdrawing from 6. Apparatus for separating particles of a nonmagnetic material according to density and shape parameters comprising a tube containing a suspension of magnetic material colloidally dispersed in a liquid, ,a first electromagnetic coil disposed along the length of said tube for producing an electromagnetic field in said suspension, means for varying the strength of said electromagnetic field along the length of said tube to cause the viscosity of said suspension to vary progressively along the length of .said tube, means for introducing'said nonmagnetic material in said tube to cause said nonmagnetic material to distribute itself in .said variable viscosity suspension in accordance with its density and shape parameters, a plurality of second electromagnetic coils disposed about said tube at zones spaced along the length thereof, means for energizing said second coils to produce a plurality of spaced electromagnetic fields which effectively solidify said suspension into a plurality of discs at said zones, means for withdrawing from .said tube the portion of said suspension, andiparticles of nonmagnetic material between said discs, and means for separating said particles of nonmagnetic material from said suspension in said withdrawn portion.

7. Apparatus for separating particles of a nonmagnetic material according to density and shape parameters comprising a tube containing a suspension of magnetic material colloidally dispersed in a liquid, a first electromagnetic coil disposed along the length of said tube for producing an electromagnetic field in said suspension, means for varying the strength of said electromagnetic field along the length of said tube to cause the viscosity of said suspension to vary progressively along the length of said tube, means for introducing said nonmagnetic material in said tube to cause said nonmagnetic material to be distributed in said variable viscosity suspension in accordance with its density and shape parameters, a plurality of second electromagnetic coils disposed about said tube at zones spaced along the length thereof, means for energizing said second coils to produce a plurality of spaced elect romagnetic fields of greater strength than said first field to eifectively solidify said suspension into aplurality of discs at said zones, and means for withdrawing f rom said tube the portion of said suspension and particles of nonmagnetic material between said discs.

8. Apparatus for separating particles of a nonmagnetic material according to density and shape parameters comprising a nonmagnetic tube containing a suspension ofmagnetic material colloidally dispersed in a liquid, 8. first electromagnetic coil disposed along the length of said tube for producing an electromagnetic field in said suspension, means for varying the strength of said electro magnetic field along the length of said tube to cause the viscosity of said suspension to vary'progressively along the length of said tube, means for introducing said nonmagnetic material in said tube to cause said nonmagnetic material to distribute itself said variable viscosity suspension in accordance with its density and shape parameters, a plurality of second electromagnetic coils disposed about said tube at zones spaced along the length thereofl-means for energizing said second coils to produce a plurality of spaced electromagnetic fields which efiectively solidify said suspension into a plurality of discs .at said zones, and a plurality of spigots on said tube between said second coils for withdrawing from said tube the portions of said suspension and particles of nonmagnetic material between said discs.

' 9. Apparatus for separating particles of a nonmagnetic material according to density and shape parameters comprising a tube containing a suspension of magnetic material colloidally dispersed in a liquid, a first electromagnetic coil disposed along the length of said tube 'for producing an electromagnetic field in said suspension, means for varying the strength of said electromagnetic field along the length of said tube to cause the viscosity of said suspension to vary progressively along the length of said tube, means for introducing said nonmagnetic material in said tube to cause said nonmagnetic material to distribute itself in said variable viscosity suspension in accordance with its density and shape parameters, a plurality of second electromagnetic coils disposed about said tube at zones spaced along the length thereof, means for energizing said second coils to produce a plurality of spaced electromagnetic fields which efiectively solidify said suspension into a plurality of discs at said zones, a plurality of spigots in said tube between said second coils for withdrawing from said tube the portions of said suspension and particles of nonmagnetic material between said discs, electromagnetic separation means for removing said mag netic material from said withdrawn suspension, and means for separating said nonmagnetic particles from said liduid.

10. Apparatus: for separating particles of a nonmagnetic material according to density and shape parameters comprising a tube containing a suspension of magnetic material colloidally dispersed in a liquid, a first electromagnetic coil disposed along the length of said tube for producing an electromagnetic field in said suspension, means for varying the strength of said electromagnetic field along the length of tube to cause the viscosity of said suspension to vary progressively along the length of said tube, means'for introducing said particles of nonmagnetic material in said tube to cause said nonmagnetic material to be distributed in said variable viscosity suspension in accordance with its density and shape parameters, a plurality of second electromagnetic coils dis posed about said tube at zones spaced along the length thereof, means for energizing said second coils to produce a plurality of spaced electromagnetic fields which increase the viscosity of said suspension at said zones, and meansfor withdrawing from said tube the portion of said suspension and particles of nonmagnetic material between said zones.

11. The method of separating particles of a nonmagnetic material according to density and shape parameters comprising the steps of forming a column of a suspension of a magnetic material colloidally dispersed in a liquid, applying a first electromagnetic field to said suspension, varying the strength of said first field along the length of said column to cause the viscosity of said suspension to vary progressively along the length of said column, introducing said material to be separated in the top of said column to cause said nonmagnetic material to distribute itself in said variable viscosity suspension in ac cordance with'its density and shape, applying a second electromagnetic field to at least two spaced-apart zones along the'length of said column to increase the viscosity of said suspension at said zones, and withdrawing from said column the suspension and particles of nonmagnetic material between said zones.

12. The method of separating particles of a nonmagnetic material according to density and shape parameters comprising the steps of forming a column of a suspen sion of magnetic material colloidally dispersed in a liquid, applying a first electromagnetic fieldto' said suspension, varying the strength of said first field along the length of said column to cause the viscosity of said sus pension to vary progressively along the length of said column, inserting said material to be separated in the top of said column to cause said particles todistribute themselves in said variable viscosity suspension in accordance with their density and shape, varying the strength of said first field as said particles distribute themselves in said suspension, applying a second electromagnetic field to at least two spaced-apart zones along the length of said column to effectively solidify said suspension at said zones, and withdrawing from said column the suspension and particles of nonmagnetic material between said efiectively solidified zones. l i

References Cited in the file of this patent 

